The question of the possible polyploidy of RNA tumor viruses will be examined by determining whether major redundancies can be detected in the 70S RNA. The 4S RNA which serves as the primer for the initiation of RNA-directed DNA synthesis will be more fully characterized, including its amino-acid-accepting specificity, and the structural features which govern its binding to 70S RNA. The possible role of the virion nucleotidyl transferase in the functional adaptation of the primer molecule will be explored. The factors which regulate the expression of viral genes in normal, transformed non-producing, and virus-producing cells will be investigated.